Low Energy House - Double Glazed Windows - Double Glazing
The amount of heat lost through the windows and doors of a home can be as much as 25 per cent of the total heat loss. To save energy and improve comfort, old and badly fitting window frames should be replaced with energy efficient, double glazed windows
High Performance Double Glazed Windows
Expertly designed, assembled and installed double glazed windows will significantly reduce
energy usage. Modern energy efficient windows offer extraordinary thermal performance.
Replacement Double Glazed Windows - Pay Back
If replacement windows are being fitted then the extra cost of specifying
and fitting energy efficient double glazed windows is small and the savings and benefits are significant.
Opportunities to replace windows occur infrequently so it is sensible to fit windows manufactured to
the highest technical standards. It is estimated that in an average dwelling a
replacement window will pay for itself in energy savings within six years.
Energy Efficient Double Glazing
A double glazed unit consists of two sheets of glass separated by an air gap. The two panes
of glass are kept apart by spacers and the edges are sealed. The air gap provides the insulating layer that slows down the heat loss and reduces the opportunity for condensation to form.
Low E Glass for Double Glazing
In order to achieve the U-values required by the building regulations, low emissivity glass must be used.
Vacuum Glazed Windows
The world’s first commercially available vacuum glazing offers the thermal performance of conventional double glazing, with the same thickness as a single pane of glass.
Double Glazed Window Frames
Heat loss occurs through the window frame as well as through the glass. Window
frames and sashes are available in a variety of materials with differing rates of conductivity. Domestic
windows are generally manufactured from low conductivity materials, like from timber, pvc-u
(u-pvc), glass fibre and composites. Insulated hollow frames further reduce
heat loss and improve comfort. Frames made from aluminium should have a thermal
break incorporated between the glass and the metal.
High Performance Double Glazing Window Frame Profiles
Over a period of years, window frame profiles have been developed to make them
more efficient in resisting the weather and more economical in the use of material. The positioning
and size of capillary grooves and drips are strategically important in restricting the ingress of water
and ensure that, if water does get in, it can safely drain away to the outside.
Draught Prevention from Double Glazed Windows
In cold weather, warm air from inside the home passes naturally through the window to the cold
air outside. The escaping warm air draws in cold air from the outside causing draughts. To resist this effect,
components of the window assembly must be fitted as tightly as possible to keep out the wind and
Draught Proofing the Opening Sash of a Double Glazed Window
Well designed windows have durable weather seals all around the rebate of the frame. Casement windows
are the most effective design for high performance windows as the seals are fitted into grooves and
effective closing devices compress the sashes against them. For high performance casement windows,
good quality silicone rubber seals are generally the most durable.
Draught Proofing the Frame
Silicone sealant is generally used for filling irregular gaps between casement windows and the
reveals of the brickwork opening. Silicone sealant is supplied in cartridges and applied using a
Ventilation must be provided for one or more of the following purposes:
- Provision of outside air for breathing
- Dilution and removal of airborne pollutants, including odours
- Control of excess humidity; arising from water vapour in the indoor air
- Provision of air for fuel burning appliances
Trickle Vents in Double Glazed Window Frames
It is important that ventilation is controllable so that reasonable indoor
air quality can be maintained and energy waste avoided. These controls can either be manual
(i.e. operated by the occupant) or automatic. Manually controlled trickle ventilators (the most
common type of ventilators) can be located over the window frames, in window frames, just above
the glass or directly through the wall.
Ventilation is required to simply remove ‘stale’ indoor air from the building
and replace it with ‘fresh’ outside air. Typically, vents are positioned 1.7m above floor level to
avoid discomfort due to cold draughts. These ventilators often incorporate a simple flap that
allows users to shut off the ventilation provided, depending on the weather conditions.
Double Glazed Replacement Windows and the Building Regulations
Heat loss is normally measured by the thermal transmittance or U-value,
usually expressed in Wm²K. In its most basic terms, the lower the U-value, the greater the
thermal insulation will be.
There are three alternatives ways of demonstrating compliance with Building
- A whole window U-value of 2.0 Wm²K
- A glass centre pane U-value of 1.2 Wm²K
- A window energy rating of band E
Triple Glazed Windows
Expertly designed assembled and installed triple glazed windows will
significantly reduce energy usage in a new dwelling.
Low E Glass
In order to achieve the U-values required by the building regulations low E glass must
be used in triple or double glazed units.
If you have one or more of the windows replaced in your home then Building Regulations will apply to
the work. If the installer you employ is registered you will not have to involve the Building Control
Service. On completion of the work the registered installer must give your local authority a
certificate confirming that the work complies with Building Regulations
Low Energy Windows - Double Glazed Units - Low E Glass